Ignition device for spark ignition engines

ABSTRACT

The invention relates to an ignition device for an Otto engine, comprising an ignition coil, a printed circuit board, which carries a control circuit with a power transistor, a plastic housing, in which the ignition coil and the printed circuit board are arranged, and a thermal dissipation element, which protrudes through a wall of the plastic housing. In accordance with this disclosure, the printed circuit board carries a cooling body, which is plugged together with the thermal dissipation element to form a thermal bridge, which dissipates thermal losses of the control circuit out from the plastic housing.

RELATED APPLICATIONS

This application claims priority to DE 10 2012 107642.1, filed Aug. 21,2012 and DE 10 2012 111234.7, filed Nov. 21, 2012, which are herebyincorporated by reference in their entirety.

BACKGROUND

The invention relates to an ignition device for an Otto engine.

One ignition device known in the art is disclosed in DE 10 2010 007 007A1. With ignition devices of this type, it is possible to generate ahigh voltage for a spark plug from an on-board power supply systemvoltage of a vehicle battery. The ignition coil of such an ignitiondevice operates here by the principle of a transformer, that is to sayit has a primary winding that is fed by a vehicle battery, and asecondary winding that is connected to a spark plug.

A thermal loss caused by the currents involved in the voltagetransformation and by magnetic fields leads to a considerabletemperature load of ignition devices. In addition, there is also aconsiderable thermal loss in the control circuit of the ignition device,for example, caused by power transistors, which are used to switch thecurrents.

So that the control circuit of an ignition device can functioncorrectly, it has to be cooled or the thermal loss produced by thecontrol circuit has to be removed from the housing of the ignitiondevice. For this purpose, it is known from DE 10 2010 007 007 A1 tofasten a metal thermal dissipation element to power transistors of thecontrol circuit, said thermal dissipation element protruding from thehousing and being fastened by a flange on an engine block so that thecoolant of the engine can also cool the thermal dissipation element.

SUMMARY

The present invention provides a way in which the control circuit of anignition device for an Otto ignition engine can be sufficiently cooledwith lower manufacturing effort.

An ignition device according to this disclosure has a cooling body,which is plugged together with a thermal dissipation element protrudingthrough a housing wall of the ignition device to form a thermal bridge.This thermal bridge conducts thermal losses of the control circuit tothe outside of the housing of the ignition device. The plugging togetherof two components for thermal dissipation enables considerably simplermanufacture compared to the production of a single component, which isattached to a power transistor and extends through the housing, like isknown from DE 10 2010 007 007 A1.

In accordance with an advantageous refinement of this disclosure, thecooling body is soldered onto a metal surface of the printed circuitboard. It is also possible to attach the cooling body on the powertransistor or another structural element of the control circuit,however, the manufacturing process can be considerably facilitated ifthe cooling body is soldered onto a metal surface of the printed circuitboard. The cooling body can then be soldered onto the printed circuitboard, similarly to other circuit elements, for example, like an SMD(surface mounted device). The metal surface of the printed circuit boardis thus itself used to dissipate thermal losses to the cooling body.

The cooling body and the thermal dissipation element may form a tongueand groove connection. The tongue can be clamped in the groove. Thereby,a good connection that conducts heat efficiently can be achieved. Thecooling body may provide the tongue and the thermal dissipation elementthe groove of the tongue and groove connection. It is also possible thatthe thermal dissipation element provides the tongue and the cooling bodythe groove of the tongue and groove connection.

In a further advantageous refinement of this disclosure, the coolingbody is a strip bent in a U-shaped manner having two branches andholding the thermal dissipation element between its two branches. One ofthese two branches faces towards the printed circuit board, for example,is soldered thereto or to a power transistor. The other branch facesaway from the printed circuit board. Such a tab can be produced costeffectively from sheet metal. The shape of a strip bent in a U-shapedmanner has the advantage here that one of the two branches can receivethe thermal loss over a large area, for example, since the branch issoldered onto a metal face of the printed circuit board or onto thepower transistor of the control circuit. The strip bent in a U-shapedmanner additionally enables a plug-in connection with the thermaldissipation element in a simple manner. An extension, for example, asheet metal strip of the thermal dissipation element, can be pluggedbetween the two branches, where it is held in a clamped manner. Goodplanar contact between the cooling body and the thermal dissipationelement is thus achieved. The cooling body can therefore deliver heateffectively to the thermal dissipation element, which then conducts thethermal loss out from the housing.

In a further advantageous refinement of this disclosure, the powertransistor is coupled to a further cooling body. The further coolingbody can be arranged completely in the plastic housing and can deliverthermal losses of the power transistor to a wall of the plastic housing,for example, by means of a sheet metal portion that bears against a wallor extends along a wall of the plastic housing. The further cooling bodycan be attached directly to the power transistor. The further coolingbody is preferably attached to the printed circuit board however, forexample, is soldered onto the printed circuit board and/or is pluggedvia extensions into openings in the printed circuit board. It isparticularly advantageous to arrange the printed circuit board betweenthe power transistor and the further cooling body.

BRIEF DESCRIPTION OF DRAWINGS

The above-mentioned aspects of exemplary embodiments will become moreapparent and will be better understood by reference to the followingdescription of the embodiments taken in conjunction with theaccompanying drawings, wherein:

FIG. 1 shows an illustrative embodiment of an ignition device withopened housing without potting;

FIG. 2 shows a detail of a sectional view of FIG. 1; and

FIG. 3 shows the printed circuit board of the ignition device withcontrol circuit, cooling body and thermal dissipation element.

DETAILED DESCRIPTION

The embodiments described below are not intended to be exhaustive or tolimit the invention to the precise forms disclosed in the followingdetailed description. Rather, the embodiments are chosen and describedso that others skilled in the art may appreciate and understand theprinciples and practices of the present invention.

The ignition device illustrated in the figures has a plastic housing 1,in which an ignition coil 2 with primary and secondary windings and alsoa printed circuit board 3, which carries a control circuit, arearranged. The plastic housing 1 comprises a plug connector 4 forconnection of the ignition device to the on-board power supply of avehicle.

The control circuit contains a power transistor 5 and thereforegenerates a considerable thermal loss during operation. In order todissipate this loss, a cooling body 6 is soldered onto a metal surface,generally a copper surface, of the printed circuit board 1, for example,by means of SMD technology. The cooling body 6 is plugged together witha thermal dissipation element 7, which protrudes through a wall of theplastic housing 1. The cooling body 6 and thermal dissipation element 7together form a thermal bridge, which dissipates the thermal loss of thecontrol circuit outside of the plastic housing 1. Waste heat of thecontrol circuit, in particular, of the power transistor 5, thereforefirst flows over the copper surface of the printed circuit board 3 tothe cooling body 6, and from there flows over the thermal dissipationelement 7 and out from the housing 1.

The thermal dissipation element 7 may be embedded in a wall of theplastic housing 1, for example, by producing the plastic housing 1 bymeans of injection molding and, in so doing, insert molding the thermaldissipation element 7 with plastic. The thermal dissipation element 7 isintended to be fastened on an engine block of a vehicle. To this end,the thermal dissipation element 7 can be rigidly connected over a largearea to a bushing 10. It is also possible for the thermal dissipationelement 7 to form an eyelet or bushing 10. By means of this eyelet orbushing 10, the thermal dissipation element can be pushed onto a pin ofthe engine block provided for this purpose and can thus be cooled bycoolant flowing through the engine block.

The cooling body 6 soldered onto the metal surface of the printedcircuit board 3 is a strip bent in a U-shaped manner, which comprisestwo branches. One of these branches is soldered to the metal surface ofthe printed circuit board 3. The other branch, which faces away from theprinted circuit board 3, may comprise an erect end portion 6 a, in orderto facilitate the insertion of a portion 7 a of the thermal dissipationelement 7. The thermal dissipation element 7, for example, may comprisea tongue or strip-shaped portion 7 a, which is clamped between the twobranches of the cooling body 6.

The cooling body 6 and the thermal dissipation element 7 form a tongueand groove connection, wherein the tongue is clamped in the groove. Thegroove is provided by the U-shaped strip.

In the illustrative embodiment shown, the branch of the cooling body 6facing away from the printed circuit board 3 comprises a protrusion 6 b,which faces towards the other branch and facilitates the fixing of thethermal dissipation element 7. The cooling body 6 is preferably arrangedon the same side of the printed circuit board 3 as the power transistor5, but may also be on the opposite side.

Both the thermal dissipation element 7 and the cooling body 6 can beproduced cost effectively from sheet metal.

The power transistor 5 of the control circuit may additionally becoupled to a cooling body 8. In the illustrative embodiment shown, thepower transistor 5 is coupled via thermal conduction paths 9 to thecooling body 8, which is arranged in the plastic housing 1 on the sideof the printed circuit board 3 facing away from the power transistor 5.An additional cooling body 8 may also be arranged however at anotherlocation in the plastic housing 1.

The cooling body 8 typically has a sheet metal portion, which forms acooling face bearing against a wall of the plastic housing 1. Forexample, the sheet metal portion can bear resiliently against thehousing wall or can extend at least along the housing wall by beingfastened via a bent portion to the printed circuit board 3. The coolingbody 8 can be produced cost effectively as a sheet metal part that plugsinto the printed circuit board 3 via extensions and is thus coupledthermally to the power transistor 5.

While exemplary embodiments have been disclosed hereinabove, the presentinvention is not limited to the disclosed embodiments. Instead, thisapplication is intended to cover any variations, uses, or adaptations ofthis disclosure using the general principles taught herein. Further,this application is intended to cover such departures from the presentdisclosure as come within known or customary practice in the art towhich this invention pertains and which fall within the limits of theappended claims.

What is claimed is:
 1. An ignition device for an Otto engine,comprising: an ignition coil; a printed circuit board, which carries acontrol circuit comprising a power transistor; a plastic housing inwhich the ignition coil and the printed circuit board are arranged; anda thermal dissipation element, which protrudes through a wall of theplastic housing; wherein the printed circuit board carries a coolingbody plugged together with the thermal dissipation element to form athermal bridge, which dissipates thermal losses of the control circuitfrom the plastic housing.
 2. The ignition device according to claim 1,wherein the cooling body is soldered onto a metal surface of the printedcircuit board.
 3. The ignition device according to claim 1, wherein thecooling body is arranged on the same side of the printed circuit boardas the power transistor.
 4. The ignition device according to claim 1,wherein the thermal dissipation element electrically connects thecontrol circuit to the vehicle ground potential.
 5. The ignition deviceaccording to claim 1, wherein the thermal dissipation element and thecooling body form a tongue and groove connection.
 6. The ignition deviceaccording to claim 1, wherein the thermal dissipation element clamps thecooling body or the cooling body clamps the thermal dissipation element.7. The ignition device according to claim 1, wherein the cooling body isa strip bent in a U-shaped manner having two branches holding thethermal dissipation element between the two branches.
 8. The ignitiondevice according to claim 7, wherein the thermal dissipation element isclamped between the two branches.
 9. The ignition device according toclaim 7, wherein the branch facing away from the printed circuit boardcomprises an erect end portion at its free end.
 10. The ignition deviceaccording to claim 7, wherein the branch facing away from the printedcircuit board has a protrusion facing towards the other branch.
 11. Theignition device according to claim 7, wherein the branch facing awayfrom the printed circuit board has a kink, which forms a protrusionfacing towards the other branch.
 12. The ignition device according toclaim 1, wherein the thermal dissipation element comprises an eyelet forfastening the ignition device on an engine block.
 13. The ignitiondevice according to claim 1, wherein the cooling body and the thermaldissipation element are formed from sheet metal.
 14. The ignition deviceaccording to claim 1, wherein the power transistor is coupled to afurther cooling body.
 15. The ignition device according to claim 14,wherein the printed circuit board is arranged between the furthercooling body and the power transistor.
 16. An ignition device for anOtto engine, comprising: an ignition coil; a printed circuit boardcarrying a control circuit comprising a power transistor; a plastichousing in which the ignition coil and the printed circuit board arearranged; a thermal dissipation element protruding through a wall of theplastic housing; and a cooling body carried by the printed circuitboard; wherein one of the thermal dissipation element and cooling bodyis clamped to the other to form a thermal bridge, whereby heat generatedby the control circuit is transferred outside of the plastic housing.17. The ignition device according to claim 16, wherein the cooling bodycomprises a strip bent in a U-shape having two branches and the thermaldissipation element is clamped between the two branches.
 18. Theignition device according to claim 17, wherein the branch facing awayfrom the printed circuit board comprises an erect end portion at itsfree end.
 19. The ignition device according to claim 17, wherein thebranch facing away from the printed circuit board has a protrusionfacing towards the other branch.
 20. The ignition device according toclaim 17, wherein the branch facing away from the printed circuit boardhas a kink, which forms a protrusion facing towards the other branch.